The two t examples I see on a lot of lists of hated characters are Kagome Higurashi and Shinji Ikari I like both of them but the hatedom they have is epic in some circles. As far as charcters that desrve to be hated one word Shira (from Blade of The Immortal) Examples of Shira's evil listed below not for the faint of heart.

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murdering a prostitute (who had just been introduced as a Hooker With A Heart Of Gold who was just in the business to pay for her mother's medicine) supposedly because she didn't have the information she wanted. Then, the morning after he joins up with heroes Manji and Rin, he gives Rin a motivational speech over breakfast, and then reveals that they've been eating the stray dog she had befriended the night before. After that, he and Rin are attacked by a pair of assassins, who Shira kills, but not before savagely, gleefully torturing one with his saw-edged sword. He then turns to the unarmed woman who had led them into the trap and tortured her as well when Rin turns on him. Would've ended badly if Manji hadn't shown up and cut his hand off. He runs off and isn't seen for a while... until he comes back for revenge against Manji, having turned his arm stump into a weapon by carving the flesh off the end and sharpening the bones. He battles Manji's companion Magatsu, the friend of the aforementioned sweet little prostitute, and reveals to him that the reason he killed her wasn't because of information, it was because he liked cutting up women while he has sex with them, because it made their muscles seize up... all of them. He finally gets his other hand cut off and falls down a waterfall... but the brutalities still keep coming as Shira is revealed to be still alive (now missing both hands and an eye, which he claims to have replaced with a weapon) having been salvaged by his employers. His employer then asks if he's chosen a new set of hands yet, and we see a dead hooker and savaged-looking young boy in Shira's cell. With dialogue implying that he raped both of them all night long, Shira says the boy will be his hands. Shira continues to use him as his 'hands' and makes him a sex toy in exchange for helping him with revenge on Manji who killed his father (who unknown to the boy, was quite the bastard himself who'd raped Rin's mother). Then he mutilates and rapes his former comrade Hyakurin, a PREGNANT WOMAN and tortures Rin by stripping her of everything but an open shirt and tying huge rocks to her feet and leaving her tied to a dock, half submerged in water. In winter.